Cavity-Enhanced Fluorescence in Colliding Droplets of Rhodamine 6G Aqueous Solutions

A liquid droplet can act as a microscale high-Q opticalcavityvia a whispering gallery mode, where light resonates with enhancedintensity. A collision of two droplets temporarily exhibits a uniquemorphology, which provides a more effective optical cavity than asingle droplet. We investigated the mechanisms of cavity-enhancedfluorescence in colliding droplets of aqueous rhodamine 6G. Laser-excitedspectra and fluorescence generation times were acquired. The fluorescencespectra had two peaks: one attributed to amplified spontaneous emission(ASE) and the other to lasing. The lasing generation time had a longerdelay relative to that of ASE, which indicated that it required alonger propagation distance for the positive feedback. Overall, thisprovides a basis for the development of a highly efficient dye laserusing colliding droplets.